phpman > man > sg_reset(8)

SG_RESET(8)                                   SG3_UTILS                                  SG_RESET(8)



NAME
       sg_reset - sends SCSI device, target, bus or host reset; or checks reset state

SYNOPSIS
       sg_reset  [--bus]  [--device] [--help] [--host] [--no-esc] [--target] [--verbose] [--version]
       DEVICE

DESCRIPTION
       The sg_reset utility with no options (just a DEVICE) reports on the reset state  (e.g.  if  a
       reset  is underway) of the DEVICE. When given a --device, --target, --bus or --host option it
       requests a device, target, bus or host reset respectively.

       A device reset is applied to the Logical Unit (LU) corresponding to DEVICE. It is most likely
       implemented  by  a  Low  level  Driver (LLD) in Linux as a LOGICAL UNIT RESET task management
       function.

       The ability to reset a SCSI target was added in Linux kernel 2.6.27 .  A  LLD  may  send  Low
       level Drivers (LLDs) the I_T NEXUS RESET task management function. Alternatively it may use a
       transport mechanism to do the same thing (e.g. a hard reset on the link containing a SAS tar‐
       get).

       In  the Linux kernel 2.6 and 3 series this utility can be called on sd, sr (cd/dvd), st or sg
       device nodes; if the user has appropriate permissions.

       Users of this utility can check whether a reset recovery is already underway before trying to
       send  a  new  reset with this utility. Calling this utility with no options, just the DEVICE,
       will do such a check.

OPTIONS
       -b, --bus
              attempt a SCSI bus reset. A bus reset is a SCSI Parallel Interface (SPI)  concept  not
              found  in  modern  transports.  A recent LLD may implement it as a series of resets on
              targets that might be considered as siblings to the target on the DEVICE path.

       -d, --device
              attempt a SCSI device reset. This would typically involve sending a LOGICAL UNIT RESET
              task management function to DEVICE.

       -z, --help
              print the usage message then exit.

       -H, --host
              attempt  a  host  reset. The "host" in this context is often called a Host Bus Adapter
              (HBA) and contains one or more SCSI initiators.

       -N, --no-esc
              without this option, if a device reset (--device) fails then it  will  escalate  to  a
              target  reset.  And  if a target reset (--target) fails then it will escalate to a bus
              reset. And if a bus reset (--bus) fails then it will escalate to a  host  reset.  With
              this  option  only the requested reset is attempted. An alternate option name of --no-
              escalate is also accepted.

       --no-escalate
              The same as -N, --no-esc.

       -t, --target
              attempt a SCSI target reset. A SCSI target contains one or more LUs. This would  typi‐
              cally  involve  sending a I_T NEXUS RESET task management function to DEVICE There may
              be a transport action that is equivalent (e.g.  in SAS a hard reset on the  link  that
              contains the target).

       -v, --verbose
              increase the degree of verbosity (debug messages).

       -V, --version
              prints the version string then exits.

NOTES
       The  error recovery code within the Linux kernel (SCSI mid-level) when faced with a SCSI com‐
       mand timing out and no response from the device (LU) does the following. First it tries a de‐
       vice  reset  and if that is not successful tries a target reset. If that is not successful it
       tries a bus reset. If that is  not  successful  it  tries  a  host  reset.  The  "device,tar‐
       get,bus,host"  order  is  the  reset escalation that the --no-esc option attempts to stop. In
       large storage configurations the escalation may be (very) undesirable.

       This utility calls the SG_SCSI_RESET ioctl and as of lk 3.10.7 the  --no-esc  option  is  not
       supported. Patches to implement this functionality may be accepted in lk 3.18 or 3.19 .

       SAM-4  and 5 define a hard reset, a LOGICAL UNIT RESET and a I_T NEXUS RESET. A hard reset is
       defined to be a power on condition, a microcode change or a transport  reset  event.  LOGICAL
       UNIT  RESET  and  I_T NEXUS RESET can be requested via task management functions (and support
       for LOGICAL UNIT RESET is mandatory). In Linux the SCSI subsystem leaves it up to the LLDs as
       to exactly what type (if any) of reset is performed.  The "bus reset" is SCSI Parallel Inter‐
       face (SPI) concept that may not map well to recent SCSI transports so it may be a dummy oper‐
       ation.  A  "host  reset" attempts to re-initialize the HBA that the request passes through en
       route to the DEVICE. Note that a "host reset" and a "bus reset" may cause collateral damage.

       This utility does not allow individual SCSI commands to be aborted. SAM-4 defines ABORT  TASK
       and ABORT TASK SET task management functions for that.

       Prior  to SAM-3 there was a TARGET RESET task management function. And in SAM-4 I_T NEXUS RE‐
       SET appeared which seems closely related: the "I_T" stands for Initiator-Target.

       Transports may have their own types of resets not supported by this utility.  For example SAS
       has  a  link  reset in which both ends of a physical link (e.g.  between a SAS expander and a
       SAS tape drive) renegotiate their connection.

       Prior to version 0.57 of this utility the command line had short options only  (e.g.  -d  but
       not  --device). Also -h invoked a host reset while in the current version -h is equivalent to
       --help and both -H and --host invoke a host reset. For backward compatibility define the  en‐
       vironment  variable  SG3_UTILS_OLD_OPTS  or SG_RESET_OLD_OPTS . In this case -h will invoke a
       host reset and the output will be verbose as it  was  previously  (equivalent  to  using  the
       --verbose option now).  For example:

           SG_RESET_OLD_OPTS=1 sg_reset -h /dev/sg1
       sg_reset: starting host reset
       sg_reset: completed host reset

ENVIRONMENT VARIABLES
       Since   sg3_utils  version  1.23  the  environment  variables  SG3_UTILS_OLD_OPTS  or  SG_RE‐
       SET_OLD_OPTS can be given. When either is present this utility will expect the older  command
       line options as outlined in the NOTES section.

AUTHORS
       Written by Douglas Gilbert.

COPYRIGHT
       Copyright © 1999-2017 Douglas Gilbert
       This software is distributed under the GPL version 2. There is NO warranty; not even for MER‐
       CHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.



sg3_utils-1.43                              October 2017                                 SG_RESET(8)